Linear accelerators used for radiotherapy delivery are equipped with a collimation system that is designed to block selected portions of the radiation beam. FIG. 1 shows an example collimator system 10 having two sets of orthogonally positioned jaws 110 and 115 positioned to limit the radiation beam aperture into a rectangular shape and a multileaf collimator (MLC) 100 having two banks of collimator leaves 120 and 125 which approach independently from the x-directions (in some collimator systems, the lower (x) jaws are replaced by the MLC). The controllable placement of each of the collimator leaves allows for more precise collimation with arbitrary shapes.